Spectroscopic studies of laboratory generated polar stratospheric cloud particles.

A new approach has been developed to calculate wavelength-dependent complex refractive indices from spectral data of laboratory generated mimic polar stratospheric cloud (PSC) particles. Previous determinations of refractive index for mimic PSC aerosols and thin-films have used Kramers-Kronig based methods. To determine the refractive index this approach requires two aerosol spectra of the same composition, but with different mean radii; i.e. one spectrum of small particles with a negligible scattering component, and another with larger particles and stronger scattering component. Our analysis takes a more fundamental approach by first determining the complex dielectric constant, which can then be related to the complex refractive index at a given wavelength. The dielectric constant is calculated with a damped harmonic oscillator model using band parameters for each oscillator. This results in a much smaller number of unknowns for the retrieval analysis, enabling determination of refractive index from a single infrared extinction spectrum and negating the need for two spectra of the same composition but different mean radii, which can be difficult to obtain experimentally. Preliminary results are presented from laboratory measurements of supercooled ternary (H2SO4 / HNO3 / H2O) solution (STS) aerosols